Re: [PATCH net-next] tcp: Accept ECT on SYN in the presence of RFC8311

[Yuchung Cheng]

On Wed, Apr 3, 2019 at 8:39 AM Neal Cardwell <ncardwell@xxxxxxxxxx> wrote:
>
> On Wed, Apr 3, 2019 at 9:50 AM Tilmans, Olivier (Nokia - BE/Antwerp)
> <olivier.tilmans@xxxxxxxxxxxxxxxxxxx> wrote:
> >
> > Linux currently disable ECN for incoming connections when the SYN
> > requests ECN and the IP header has ECT(0)/ECT(1) set, as some
> > networks were reportedly mangling the ToS byte, hence could later
> > trigger false congestion notifications.
> >
> > RFC8311 Â4.3 relaxes RFC3168's requirements such that ECT can be set
> > one TCP control packets (including SYNs). The main benefit of this
> > is the decreased probability of losing a SYN in a congested
> > ECN-capable network (i.e., it avoids the initial 1s timeout).
> > Additionally, this allows the development of newer TCP extensions,
> > such as AccECN.
> >
> > This patch relaxes the previous check, by enabling ECN on incoming
> > connections using SYN+ECT if at least one bit of the reserved flags
> > of the TCP header is set. Such bit would indicate that the sender of
> > the SYN is using a newer TCP feature than what the host implements,
> > such as AccECN, and is thus implementing RFC8311. This enables
> > end-hosts not supporting such extensions to still negociate ECN, and
> > to have some of the benefits of using ECN on control packets.
> >
> > Signed-off-by: Olivier Tilmans <olivier.tilmans@xxxxxxxxxxxxxxxxxxx>
> > Suggested-by: Bob Briscoe <research@xxxxxxxxxxxxxx>
> > Cc: Koen De Schepper <koen.de_schepper@xxxxxxxxxxxxxxxxxxx>
>
> Acked-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Acked-by: Yuchung Cheng <ycheng@xxxxxxxxxx>

>
> Thank you for this patch, Olivier and Bob.
>
> thanks,
> neal